linux-kernel - Re: [PATCH] usb: ulpi: call put_device if device

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Message-ID: <20150723020440.GB16806@saruman.tx.rr.com>
Date:	Wed, 22 Jul 2015 21:04:40 -0500
From:	Felipe Balbi <balbi@...com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	ChengYi He <chengyihetaipei@...il.com>,
	Felipe Balbi <balbi@...com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: ulpi: call put_device if device_register fails

On Wed, Jul 22, 2015 at 02:39:34PM -0700, Greg Kroah-Hartman wrote:
> On Tue, Jun 23, 2015 at 01:57:38PM +0300, Heikki Krogerus wrote:
> > On Fri, Jun 19, 2015 at 01:12:36AM +0800, ChengYi He wrote:
> > > put_device is required to release the last reference to the device.
> > > 
> > > Signed-off-by: ChengYi He <chengyihetaipei@...il.com>
> > > ---
> > >  drivers/usb/common/ulpi.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/usb/common/ulpi.c b/drivers/usb/common/ulpi.c
> > > index 0e6f968..bd25bdb 100644
> > > --- a/drivers/usb/common/ulpi.c
> > > +++ b/drivers/usb/common/ulpi.c
> > > @@ -184,8 +184,10 @@ static int ulpi_register(struct device *dev, struct ulpi *ulpi)
> > >  	request_module("ulpi:v%04xp%04x", ulpi->id.vendor, ulpi->id.product);
> > >  
> > >  	ret = device_register(&ulpi->dev);
> > > -	if (ret)
> > > +	if (ret) {
> > > +		put_device(&ulpi->dev);
> > 
> > If device_register returns failure, put_device has already been
> > called. Check device_add in drivers/base/core.c.
> 
> Yes, please read the function, which says:
>  * NOTE: _Never_ directly free @dev after calling this function, even
>  * if it returned an error! Always use put_device() to give up your
>  * reference instead.
> 
> But, the problem is that the ulpi core doesn't "own" that struct device.
> It comes from elsewhere.  It comes from somewhere deep down in the dw3
> core, which is where I lost the path.  Something needs to be fixed in
> dwc3_probe() to properly clean up the device if it fails, which is not
> happening right now.
> 
> So this patch would actually cause much bigger problems than fixing
> anything, so it's wrong, but for a different reason than you are talking
> about here.
> 
> And ugh, the ulpi and dwc code binding together, what a mess, horrid...

any suggestions ? DWC *is* the one implementing the bus. If there's a
better way, we can certainly shuffle code around.

-- 
balbi

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